2015-03-03T22:38:48ZEffect of glass on the frictional behavior of basalts at seismic slip rateshttp://hdl.handle.net/2122/9316
Title: Effect of glass on the frictional behavior of basalts at seismic slip rates
Authors: Violay, M. E. S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Di Toro, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Nielsen, S. B.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Gilbert, B.; Géosciences Montpellier, UMR 5243, Université Montpellier II, Montpellier, France; Spagnuolo, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Azais, P.; Géosciences Montpellier, UMR 5243, Université Montpellier II, Montpellier, France; Del Gaudio, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Scarlato, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia
Abstract: We performed 31 friction experiments on glassy basalts (GB) and glass-free basalts (GFB) at slip rates up to 6.5 m s−1 and normal stress up to 40 MPa (seismic conditions). Frictional weakening was associated to bulk frictional melting and lubrication. The weakening distance (Dw) was about 3 times shorter in GB than in GFB, but the steady state friction was systematically higher in GB than in GFB. The shorter Dw in GB may be explained by the thermal softening occurring at the glass transition temperature (Tg ~500°C), which is lower than the bulk melting temperature (Tm ~1250°C) of GFB. Postexperiment microanalyses suggest that the larger crystal fraction measured in GB melts results in the higher steady state friction value compared to the GFB melts. The effect of interstitial glass is to facilitate frictional instability and rupture propagation in GB with respect to GFB.2013-12-31T23:00:00ZPore fluid in experimental calcite-bearing faults: Abrupt weakening and geochemical signature of co-seismic processeshttp://hdl.handle.net/2122/9315
Title: Pore fluid in experimental calcite-bearing faults: Abrupt weakening and geochemical signature of co-seismic processes
Authors: Violay, M. E. S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Nielsen, S. B.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Spagnuolo, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Cavallo, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia
Abstract: While it is widely recognized that fluids influence fault strength and earthquake nucleation, propagation
and arrest, their effects on co-seismic sliding friction are only conjectured. To shed light on these
effects, 55 high velocity (41ms1
) friction experiments were conducted at room temperature on
Carrara marble samples in the presence of pore fluid (up to 15 MPa pore pressure), room-humidity and
‘‘vacuum’’ (104 mbar) conditions. In all the experiments, the friction coefficient evolved from a peak
value of 0.6–0.8 to a steady-state value of 0.1 in about 1–1.5 m of slip. However, experiments
performed in the presence of pore fluid had a large and more abrupt decrease in friction at the
initiation of sliding (65% after 20 mm of slip), whereas experiments performed under vacuum and room
humidity conditions showed initial velocity-strengthening behavior followed by a more gradual
reduction in friction. This indicates that calcite-bearing rocks are more prone to slip in the presence
of water. Under room-humidity conditions, CO2 was detected during the entire duration of the
experiment. In the presence of pore fluid, HCO3
and Ca2þ were detected for slips 40.1 m. The lack
of decarbonation products (HCO3
and Ca2þ) in pore fluid experiments for slip o0.1 m implies that
the abrupt weakening is not related to decarbonation (or that the abundance of the reaction products is
below the resolution of the analytical methods). Given the modest thermal expansion of water,
the estimated thermal pressurization during the abrupt weakening appears to be negligible. Instead,
we suggest that abrupt weakening is due to subcritical crack-growth, hydrolytic weakening and brittle
failure of the asperities on the sliding surfaces. Modeling shows that the occurrence in nature of
co-seismic (water-present) decarbonation reactions similar to those triggered in the laboratory could
yield sufficient reaction product to be detected in aquifers located in the proximity of active faults.
&2012-12-31T23:00:00ZEffect of water on the frictional behavior of cohesive rocks during earthquakeshttp://hdl.handle.net/2122/9314
Title: Effect of water on the frictional behavior of cohesive rocks during earthquakes
Authors: Violay, M. E. S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Nielsen, S. B.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Gibert, B.; Géosciences Montpellier UMR5243, Université Montpellier, 2 Place Bataillon, 34095 Montpellier cedex 5, France; Spagnuolo, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Cavallo, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Azais, P.; Géosciences Montpellier UMR5243, Université Montpellier, 2 Place Bataillon, 34095 Montpellier cedex 5, France; Vinciguerra, S.; Dipartimento di Scienze della Terra, Università degli Studi di Torino, Via Valperga Caluso 35, 10125 Turin, Italy; Di Toro, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia
Abstract: Fluid-rock interactions can control earthquake nucleation and the evolution of earthquake
sequences. Experimental studies of fault frictional properties in the presence of fl uid can provide
unique insights into these interactions. We report the fi rst results from experiments performed
on cohesive silicate-bearing rocks (microgabbro) in the presence of pressurized pore fl uids (H2
O,
drained conditions) at realistic seismic deformation conditions. The experimental data are compared
with those recently obtained from carbonate-bearing rocks (Carrara marble). Contrary
to theoretical arguments, and consistent with the interpretation of some fi eld observations, we
show that frictional melting of a microgabbro develops in the presence of water. In microgabbro,
the initial weakening mechanism (fl ash melting of the asperities) is delayed in the presence of
water; conversely, in calcite marble the weakening mechanism (brittle failure of the asperities)
is favored. This opposite behavior highlights the importance of host-rock composition in controlling
dynamic (frictional) weakening in the presence of water: cohesive carbonate-bearing rocks
are more prone to slip in the presence of water, whereas the presence of water might delay or
inhibit the rupture nucleation and propagation in cohesive silicate-bearing rocks.2013-11-30T23:00:00ZCoseismic recrystallization during shallow earthquake sliphttp://hdl.handle.net/2122/9312
Title: Coseismic recrystallization during shallow earthquake slip
Authors: Smith, S. A. F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Di Toro, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Kim, S.; Department of Earth and Environmental Sciences, Korea University, Seoul 136-701, Republic of Korea; Ree, J.-H.; Department of Earth and Environmental Sciences, Korea University, Seoul 136-701, Republic of Korea; Nielsen, S. B.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Billi, A.; Consiglio Nazionale delle Ricerche, Istituto di Geologia Ambientale e Geoingegneria, c.o. Dipartimento Scienze della Terra, Sapienza Università di Roma, 00185 Rome, Italy; Spiess, R.; Dipartimento delle Scienze della Terra, Università degli Studi di Padova, Via G. Gradenigo 6, 35131 Padua, Italy
Abstract: Solidified frictional melts, or pseudotachylytes, remain the only unambiguous indicator of seismic slip in the geological record. However, pseudotachylytes form at >5 km depth, and there are many rock types in which they do not form at all. We performed low- to high-velocity rock friction experiments designed to impose realistic coseismic slip pulses on calcite fault gouges, and report that localized dynamic recrystallization may be an easy-to-recognize microstructural indicator of seismic slip in shallow, otherwise brittle fault zones. Calcite gouges with starting grain size <250 μm were confined up to 26 MPa normal stress using a purpose-built sample holder. Slip velocities were between 0.01 and 3.4 m s−1, and total displacements between 1 and 4 m. At coseismic slip velocities ≥0.1 m s−1, the gouges were cut by reflective principal slip surfaces lined by polygonal grains <1 μm in size. The principal slip surfaces were flanked by <300 μm thick layers of dynamically recrystallized calcite (grain size 1–10 μm) containing well-defined shape- and crystallographic-preferred orientations. Dynamic recrystallization was accompanied by fault weakening and thermal decomposition of calcite to CO2 + CaO. The recrystallized calcite aggregates resemble those found along the principal slip surface of the Garam thrust, South Korea, exhumed from <5 km depth. We suggest that intense frictional heating along the experimental and natural principal slip surfaces resulted in localized dynamic recrystallization, a microstructure that may be diagnostic of seismic slip in the shallow crust.2013-09-30T22:00:00ZGouge graphitization and dynamic fault weakening during the 2008 Mw 7.9 Wenchuan earthquakehttp://hdl.handle.net/2122/9311
Title: Gouge graphitization and dynamic fault weakening during the 2008 Mw 7.9 Wenchuan earthquake
Authors: Kuo, L.; National Taiwan University, 10617 Taipei, Taiwan; Li, H.; State Key Laboratory of Continental Tectonic and Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China; Smith, S. A. F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Di Toro, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Suppe, J.; National Taiwan University, 10617 Taipei, Taiwan; Song, S; National Taiwan University, 10617 Taipei, Taiwan; Nielsen, S. B.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Sheu, H.; National Synchrotron Radiation Research Center, 30076 Hsinchu, Taiwan; Si, J.; State Key Laboratory of Continental Tectonic and Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China
Abstract: The Longmenshan fault that ruptured during the 2008 Mw 7.9 Wenchuan (China) earthquake was drilled to a depth of 1200 m, and fault rocks including those in the 2008 earthquake slip zone were recovered at a depth of 575–595 m. We report laboratory strength measurements and microstructural observations from samples of slip zone fault rocks at deformation conditions expected for coseismic slip at borehole depths. Results indicate that the Longmenshan fault at this locality is extremely weak at seismic slip rates. In situ synchrotron X-ray diffraction analysis indicates that graphite was formed along localized slip zones in the experimental products, similar to the occurrence of graphite in the natural principal slip zone of the 2008 Wenchuan rupture. We surmise that graphitization occurred due to frictional heating of carbonaceous minerals. Because graphitization was associated with strong dynamic weakening in the experiments, we further infer that the Longmenshan fault was extremely weak at borehole depths during the 2008 Wenchuan earthquake, and that enrichment of graphite along localized slip zones could be used as an indicator of transient frictional heating during seismic slip in the upper crust.2013-10-31T23:00:00ZProgression of spontaneous in-plane shear faults from sub-Rayleigh to compressional wave rupture speedshttp://hdl.handle.net/2122/9156
Title: Progression of spontaneous in-plane shear faults from sub-Rayleigh to compressional wave rupture speeds
Authors: Liu, C.; University of Oxford; Bizzarri, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Das, S.; University of Oxford
Abstract: We investigate numerically the passage of spontaneous, dynamic in-plane shear ruptures from
initiation to their final rupture speed, using very fine grids. By carrying out more than 120 simulations, we
identify two different mechanisms controlling supershear transition. For relatively weaker faults, the rupture
speed always passes smoothly and continuously through the range of speeds between the Rayleigh and shear
wave speeds (the formerly considered forbidden zone of rupture speeds). This, however, occurs in a very short
time, before the ruptures reach the compressional wave speed. The very short time spent in this range of
speeds may explain why a jump over these speeds was seen in some earlier numerical and experimental
studies and confirms that this speed range is an unstable range, as predicted analytically for steady state,
singular cracks. On the other hand, for relatively stronger faults, we find that a daughter rupture is initiated by
the main (mother) rupture, ahead of it. The mother rupture continues to propagate at sub-Rayleigh speed and
eventually merges with the daughter rupture, whose speed jumps over the Rayleigh to shear wave speed
range. We find that this daughter rupture is essentially a “pseudorupture,” in that the two sides of the fault are
already separated, but the rupture has negligible slip and slip velocity. After the mother rupture merges with
it, the slip, the slip velocity, and the rupture speed become dominated by those of the mother rupture. The
results are independent of grid sizes and of methods used to nucleate the initial rupture.2014-10-31T23:00:00ZLinking the recurrence time of earthquakes to source parameters: A dream or a real possibility?http://hdl.handle.net/2122/9148
Title: Linking the recurrence time of earthquakes to source parameters: A dream or a real possibility?
Authors: Bizzarri, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Crupi, P.; Università degli Studi di Bari " Aldo Moro "
Abstract: By using a single-degree-of-freedom spring-slider
analog fault model, we generate a synthetic catalog of nearly 500
different seismic sequences. We explore the parameter space by
assuming different values of constitutive parameters and tectonic
environment. We also consider three different versions of the ratedependent
and state-dependent friction laws [the Dieterich-Ruina
(DR), the Ruina-Dieterich (RD) and the Chester-Higgs (CH)
models], and different approximations of the behavior of the friction
at high sliding speeds, as well as the radiation damping effects.
Our results indicate that for all the considered models, the recurrence
time (Tcycle) exhibits an inverse proportionality on the
loading rate; a linear, positive dependence on the effective normal
stress; and a linear, negative dependence on the characteristic
distance controlling the state variable evolution. These results
confirm and generalize previous studies. Remarkably, we found
here that the coefficients of proportionality strongly depend on the
adopted friction model, on the high speed behavior and on the
reference set of parameters. Notably, we also found that the positive
proportionality between Tcycle and the difference b – a,
confirmed for DR and RD laws, does not hold in general for the CH
law. Overall, we conclude that even in the simplest (and idealized)
case of characteristic earthquakes considered here, in which the
limiting cycle is reached by the system, and even in the framework
of a very simplified fault model, the possibility to a priori predict,
through an universal analytical relation, the inter-event time of an
impending earthquake still remains only a dream. On the other
hand, a numerical prediction of Tcycle would require the exact
knowledge of the rheological model (and its parameters at all times
over the entire life of the fault) and the actual state of the fault,
which indeed are often unknown.2014-09-30T22:00:00ZRake rotation introduces ambiguity in the formulation of slip-dependent constitutive models: slip modulus or slip path?http://hdl.handle.net/2122/9125
Title: Rake rotation introduces ambiguity in the formulation of slip-dependent constitutive models: slip modulus or slip path?
Authors: Bizzarri, A; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia
Abstract: The linear slip–weakening (SW) law, predicting that the traction decreases
for increasing fault slip, is one of the most widely adopted governing
models to describe the traction evolution and the stress release
processes occurring during coseismic slip failures. We will show that, contrary
to other constitutive models, the SW law inherently poses the problem
of considering the Euclidean norm of the slip vector or its cumulative
value along its path. In other words, it has the intrinsic problem of its
analytical formulation, which does not have a solution a priori. By considering
a fully dynamic, spontaneous, 3–D rupture problem, with rake
rotation allowed, in this paper we explore whether these two formulations
can lead to different results. We prove that, for homogeneous configurations,
the two formulations give the same results, with a normalized
difference less than 1%, which is comparable to the numerical error due
to grid dispersion. In particular, we show that the total slip, the resulting
seismic moment, the fracture energy density, the slip–weakening curve
and the energy flux at the rupture front are practically identical in the
two formulations. These findings contribute to reconcile the results presented
in previous papers, where the two formulations have been differently
employed. However, this coincidence is not the rule. Indeed, by
considering models with a highly heterogeneous initial shear stress distribution,
where the rake variation is significant, we have also demonstrated
that the overall rupture history is quite different by assuming the
two formulations, as well as the fault striations, the traction evolution
and the scalar seismic moment. In this case the choice of the analytical formulation
of the governing law does really matter.2014-09-30T22:00:00ZThe destiny of a clast within a molten pseudotachylyte Veinhttp://hdl.handle.net/2122/9121
Title: The destiny of a clast within a molten pseudotachylyte Vein
Authors: Bizzarri, A; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia
Abstract: Pseudotachylytes are important markers that can indicate the thermal state during a
coseismic slip failure and provide indirect information about the level of stress and
sliding velocities attained during that time window. On the other hand, survivor,
fragmented clasts embedded in the quenched material are also very important, in that
they provide information about the energy spent to create new fracture surfaces. In
this paper, I study the temperature evolution of clasts subjected to the heat
dissipated by a just-formed, molten pseudotachylyte (PT) vein. In particular, I find
the analytical solutions for the temperature evolution within the PT vein, the
surrounding, undamaged host rock, and inside a clast. According to the proposed model,
the numerical results show that the clasts tend to preferentially melt in the inner
part of the PT vein (i.e., they are completely assimilated by the PT). In contrast,
some clasts can survive far from the PT vein center. My solutions, although based upon
a simplified model, can provide a theoretical framework to predict the maximum size
of the survived clasts at a given distance from the PT center. The distribution of
these survivor clasts follows a power-law relation in terms of their radius, and its
features generally agree with field and laboratory observations.2014-09-30T22:00:00ZMonitoraggio sismico del territorio nazionale: stato dell'arte e sviluppo delle reti di monitoraggio sismicohttp://hdl.handle.net/2122/8813
Title: Monitoraggio sismico del territorio nazionale: stato dell'arte e sviluppo delle reti di monitoraggio sismico
Authors: Sergio, Guardato; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia
Abstract: Il sistema CUMAS (Cabled Underwater Module
for Acquisition of Seismological data) è un
prodotto tecnologico-scientifico complesso nato
con il Progetto V4 [Iannaccone et al., 2008] allo
scopo di monitorare l’area vulcanica dei Campi
Flegrei (fenomeno del bradisismo).
Si tratta di un modulo sottomarino cablato e
connesso a una boa galleggiante (meda elastica). Il
sistema è in grado di acquisire e trasmettere alla
sala di monitoraggio dell’OV, in continuo e in
tempo reale, sia i segnali sismologici sia quelli di
interesse geofisico ed oceanografico (maree,
correnti marine, segnali acustici subacquei,
parametri funzionali di varia natura).
Il sistema è in grado di ricevere comandi da remoto
per variare diversi parametri di acquisizione e di
monitorare un cospicuo numero di variabili di
funzionamento.
Il sistema si avvale del supporto di una boa
galleggiante attrezzata. La boa è installata a largo
del golfo di Pozzuoli (Napoli) a circa 3 km dalla
costa. Il modulo sottomarino, collegato via cavo
alla parte fuori acqua della boa, è installato sul
fondale marino a una profondità di circa 100 metri.2010-12-31T23:00:00Z